1. Field of the Invention
The present invention relates to a switching power circuit.
2. Description of the Related Art
Hitherto, a push-pull type switching power supply circuit is generally employed in a switching power circuit.
In the push-pull type switching power supply circuit there occurs a noise that influences on a radio or the like (for example, AM band) as in a switching power supply circuit having another structure. Therefore, various countermeasures for preventing the noise occurrence have been conducted in the push-pull type switching power circuit.
For example, a structure is employed in which a noise filter is added to a switching power supply circuit to prevent the noise from occurring. Also, a resonant type switching power supply circuit consisting of an LC resonant circuit is structured as disclosed in Japanese Patent Application Laid-open No. Hei 7-67334, or a secondary rectifying circuit and a tertiary rectifying circuit are added as disclosed in Japanese Patent Application Laid-open No. Hei 9-224375, to thereby prevent the noise from occurring.
However, even in the above-mentioned push-pull type switching power circuits thus structured, a new component needs to be added, resulting in such a problem that the switching power supply circuit becomes high in the costs.
The present invention has been made in order to solve the above-mentioned problem, and an object of the present invention is to provide without adding new components a switching power supply circuit that has a high effect in reducing the noise.
A switching power supply circuit according to the present invention comprises: a d.c. power supply; and a switching means having a plurality of switching elements connected to the d.c. power supply to conduct the switching operation of alternately turning on/off at a switching frequency, wherein a component of a frequency that is twice as high as the switching frequency becomes less than or equal to the component of the switching frequency in a spectrum of a current that is supplied from the d.c. power supply by making the switching elements conduct the switching operations differently from each other.